(1) Field of the Invention
This invention relates to a switching valve, and more particularly to a switching valve for switching a refrigerant passage in a refrigeration cycle of an automotive air conditioner.
(2) Description of the Related Art
In general, in an automotive air conditioner, cooling is carried out using a refrigeration cycle that circulates refrigerant, and heating is carried out using engine coolant. Recently, however, due to the improvement in combustion efficiency of the engine, the temperature of the coolant does not rise high enough to a temperature required for heating. As a result, especially when the engine is started in winter, it takes a long time before the temperature in the compartment rises, and there can be cases in which even if the temperature rises, the temperature does not reach the set-point.
To cope with the above inconvenience, it has been proposed to use high-temperature and high-pressure refrigerant discharged from the compressor in the refrigeration cycle for auxiliary heating (see e.g. Japanese Unexamined Patent Publication No. 2000-318436 (Paragraph No. [0016], FIG. 1)). More specifically, in the refrigeration cycle, high-temperature and high-pressure refrigerant adiabatically compressed by the compressor is first condensed by a condenser, and the condensed refrigerant is adiabatically expanded by an expansion valve into refrigerant at low temperature and low pressure. The expanded refrigerant is evaporated by an evaporator, and then separated into gas and liquid by an accumulator. Gaseous refrigerant obtained by the separation returns to the compressor. Although the evaporator carries out heat exchange between the low-temperature refrigerant and the air in the compartment, to thereby cool the air in the compartment, an attempt is being made to cause the high-temperature refrigerant discharged from the compressor to be introduced into the evaporator, to thereby utilize the evaporator as an air heater for auxiliary heating.
To this end, it is necessary to provide a switching valve on the discharge side of the compressor, for causing the compressed refrigerant to flow selectively toward the condenser or the evaporator. In a switching valve of this kind, a first solenoid valve is disposed between a compressor and a condenser, and a second solenoid valve is disposed between the compressor and an evaporator to thereby control the first and second solenoid valves such that the first solenoid valve is opened and the second solenoid valve is closed during cooling operation, and the first solenoid valve is closed and the second solenoid valve is opened during heating operation, whereby switching between the refrigerant passages is carried out.
As described above, two solenoid valves are required to switch between the refrigerant passages. However, a switching valve is also known which performs the switching operation with one solenoid valve (see e.g. Japanese Unexamined Patent Publication No. 2001-124440 (Paragraph Nos. [0018] to [0023], FIGS. 1 to 3)). According to this switching valve, a solenoid valve for performing opening/closing control of a refrigerant passage between a compressor and a condenser is integrally formed with a differential pressure valve that opens a refrigerant passage between the compressor and an evaporator when the differential pressure between the compressor and the condenser becomes equal to or larger than a predetermined value, with the above solenoid valve being in a closed state. The differential pressure valve comprises a valve element for sensing the differential pressure between the compressor and the condenser, a spring for urging the valve element toward a valve seat, and a diaphragm for sealing between the compressor and the condenser.
In the conventional switching valve of integral construction, however, the sealing mechanism of the differential pressure valve for opening and closing the refrigerant passage between the compressor and the evaporator is formed by the diaphragm which has small displacement stroke, and hence when an attempt is made to increase the opening stroke of the switching valve so as to reduce pressure loss in the differential pressure valve, the size of a valve construction is increased.